Our goal is to continue integrated physiological studies of the seminiferous tubules (SNT) and the epididymis using micropuncture and ultra microanalytic techniques. Specific aims include: 1) definition of in vivo concentration of important elements and organic compounds including steroid hormones and proteins in the plasma of the SNT and epididymis; 2) further studies of the tubular transport of these factors; 3) inquiry into the mechansims which regulate the intratubular concentrations and transport of these factors; 4) additional investigations of the blood-testis and blood-epididymal barrier; and 5) studies of the factors regulating the initiation of motility in epididymal spermatozoa. Techniques to be utilized include, free-flow micropuncture, split-drop micropuncture, helium glow photometry, liquid scintillation counting, spermatozoan counting, electron probe analysis, micro-gel column electrophoresis, electrophoresis gel densitometry, micro-osmometry, and possibly radio-immunoassay for steroid hormones.